Also need to check default orders for "Mul" and "Add" if they is not changed in DataPack
Mul = 20
Add = 30
Or Mul will be calculate before Add if order is not set to different values in DP.
For see default values for all stats look java.com.l2jserver.gameserver.enums.StatFunction.java

That is when "FuncAtkCritical" get order 1. So formula is called first then other values is add.
In that case we use "Add" to add (+15) that "Add" stat got order 30 what will happen if change order inside "FuncAtkCritical" to 31.
FROM

Q : In com.l2jserver.gameserver.mode.stats.functions.formulas.* Orders used in that formulas effect the other formulas?
For example order inside FuncAtkAccuracy effect in some way FuncAtkCritical?A : NoQ : Why there is some items what not use default orders and they got custom one like Jewels and Armors A :

SPOILER:

Lets take again "Maestro" again and see how Pdef and Mdef is calculate.
game\data\stats\chars\baseStats\Maestro.xml

For example to calculate base Pdef we need to sum all base Pdef so we calculate "chest + legs + head + feet + gloves + underwear + clock" in that case 31 + 18 + 12 + 7 + 8 + 3 + 1.
But we don't keep that values separated and in server start we calculate the sum and put in one variable. Later when we need to calculate base PDef we look used slots and sub value based on item.

Base PDef for Maestro will be 80, then PDef formula is called.
Why is that order 0. That is used to not made new "setGlovesDef", "setChestDef" and other values what will change base Glolves, BaseChest defence when item is used.
Add stats got order 30 so if we not change the order they will be add to late and formula will return bad stats. Using order 0 on them we put that calculation on the begining.

Coz that stat got order 0 is called before formula so we do.
80 + 47 = 127 Base PDef and then we called the PDef formula.
Few lines before calculate the stat is check if "Chest" is used, and see we put that new armor so he remove from that value base chest PDef.
127 - 31 = 96 Base PDef.
For value is used 96.

So basically that is hack to use same value in a lot places (real power of custom orders).
With MDef is the same.